The present invention relates to a superconducting switching device, and in particular to a superconducting switching device suitable for use in a flux pump, a superconducting rectifier, and a persistent current switching.
Such a superconducting switching device of the prior art is shown in FIG. 2A. In FIG. 2A, numeral 1 denotes a switching member comprising a superconducting wire, which contains Nb or Nb-1% Zr alloys. Numeral 2 denotes a coil for applying a magnetic field. And the superconducting switching device is normally used under the state that it is immersed in liquid helium
FIG. 2B shows the magnetic field versus critical current density characteristics of Nb-1% Zr which is an example of the superconducting wire 1 used in FIG. 2A. The origin side of a curve 3 exhibits a superconductive state where the electric resistance is zero. This state corresponds to the ON-state. If a current is let to flow through the magnetic field applying coil 2 to apply such a magnetic field as to cause a state located at the outside of the curve 3, the normal conductive state is caused and a finite electric resistance is generated. This state corresponds to the OFF-state. When the current flowing through the magnetic field applying coil 2 is stopped, the ON-state is restored. The ON-OFF switching operation is thus performed.
JP-A-59-111381, for example, relates to such a device or apparatus.
Since a conventional superconducting switching device is configured as described above, the electric resistivity of the switching member 1 under the normal conductive state is as small as 5 to 20 .mu..OMEGA.cm, a favorable switching effect being hardly obtained. The electric resistance can be raised by making the length of the superconducting wire long. However, this results in a drawback that the volume of the switching member 1 becomes large and the necessary dimension of the magnetic field applying coil 2 also becomes large. Further, the critical magnetic field of the switching member 1 is as large as 0.4 to 0.81 T. This results in a drawback that a large-sized magnetic field applying coil 2 is needed in order to perform normal conductive transition.